docs: def ensure_unique(qs, field_name, value, exclude_id=None):
      """
      Makes sure that `value` is unique on model.fieldname. And nonempty.
      """
      orig = value
      if not value:
          value = "None"
      for x in itertools.count(1):
          if not qs.exclude(id=exclude_id).filter(**{field_name: value}).exists():
              break
          if orig:
              value = '%s-%d' % (orig, x)
          else:
              value = '%d' % x
  
      return value